1. Field of the Invention
The invention relates generally to global positioning using the Global Positioning System (GPS) and more particularly to systems and methods for obtaining global positioning satellite information.
2. Background
A traditional GPS receiver receives and processes specially coded satellite communication signals. The satellite signals are generated from an array of satellites that comprise the GPS system. Nominally, this array consists of 24 satellites arranged in various orbits such that between 5 and 8 satellites are visible from any point on earth. GPS receivers convert the satellite signals into position, velocity, and time estimates. Four satellites are required to compute the three position dimensions (x,y,z) as well as the time.
More and more frequently wireless communication devices, such as cellular type handsets, are incorporating GPS capability. A driving factor behind the integration of GPS into wireless communication devices is the Federal Communication Commission's (FCC's) Enhanced 911 (E911) mandate. The purpose of the FCC's E911 rules is to improve the reliability of wireless 911 service and to provide emergency service personnel with location information that will enable them to provide emergency service faster and more efficiently. Wireless communication system operators are required to provide Automatic Location Identification (ALI) as part of phase II of the E911 implementation. Incorporating GPS within wireless communication devices enables wireless communication system operators to meet the phase II requirements.
Incorporation of GPS can, however, prove taxing on the limited resources of most wireless communication devices. Size, cost, memory, and processing power are all limited resources within a wireless communication device. In order to reduce the impact of incorporating GPS capability on such resources, the wireless communication devices' GPS capability is often “network assisted.” In other words, the network portion of the wireless communication system provides information, such as acquisition assist (AA) or sensitivity assist (SA) information, that allows a wireless communication device to acquire, quickly and effectively, the GPS satellites needed to provide the requisite location information.
In a large-scale emergency, however, the network assist resources are likely to become inundated due to thousands of 911 calls. Such inundation is likely to cripple the positioning capabilities of wireless communication systems, just when they are needed most. Incorporating full GPS capability in wireless communication devices, thus eliminating the need for network assistance, can prevent this problem. But, as mentioned, such an approach is undesirable due to the negative impact it will have on the device's limited resources. Thus, the massive traffic created by a major disaster can cripple the ALI ability of conventional wireless communication systems and the only currently available solution overburdens already limited wireless communication device resources.